Now a Word from the East Coast

n the 60s and 70s loudspeaker sound came to be characterized by geographic location.

JBL, out of Los Angeles, became known as offering the “West Coast” sound while a group of Boston speaker companies, principally Acoustic Research, offered the competing “East Coast” sound.

East Coast speakers were characterized as having an in-room response that declined in the upper midrange and treble. The West Coast JBL speakers went the other way, with a prominent midrange and top-end, making them the speakers of choice for rock fans, but reviews in objective and subjective audio magazines were not very positive to models like the popular JBL L100 Century. This at a time where some noted that reviews in audio magazines were so watered down the conclusion said little more than “of all the speakers we tested, this was one of them”.

Acoustic Research Historian Tom Tyson explains the downward sloping in-room response of the AR-3 which was a very popular and positively reviewed speaker of the time:

“The on-axis output and sensitivity were often sacrificed in favor of better off-axis response. I think it was a conscious decision (fathered by AR founder Edgar Villchur with the AR-3). The AR-3a, for example, used a hard-dome tweeter that was fairly low in sensitivity, but it had superior dispersion for the time, easily the widest dispersion of any tweeter available back then. AR’s philosophy was smooth and extended acoustic-power, and their reverberant-chamber response curves validated (to them) the importance of better off-axis response, even at the expense of on-axis smoothness, since it was felt that most listening would be well back in the listening room beyond the first-arrival sound”.

Extensive anechoic and in-room measurements of the AR-3a were presented in the following AES Journal paper written by AR engineers:

Allison, Roy F.; Berkovitz, Robert “The Sound Field in Home Listening Rooms” JAES Volume 20 Issue 6 pp. 459-469; August 1972.

Chapter 18 of the 3rd edition of Dr. Floyd Toole’s book: “Sound Reproduction – The Acoustics and Psychoacoustics of Loudspeakers and Rooms” is titled “50 Years of Progress in Loudspeaker Design.” Chapter 18 shows anechoic response curves for speakers from the 60s to the 80s via on-axis along with 30 and 60 degrees off-axis plots, many for the first time. Both domestic and professional monitors are shown. What Dr. Toole shows is what he got access to at the NRC (National Research Council) of Canada’s anechoic chamber. Most were submitted by Canadian audio magazines of the day. For those who had an Advent or Dynaco A-25 as your first speakers, you will find the anechoic measurements in the Toole text. Frankly speaking, the results show that you did not lose anything when you got rid of them.

The West Coast sound is also well represented and documented in the book’s anechoic data and described by Dr. Toole. Of the JBL 4310 and L100 Century loudspeakers, Toole writes that they exhibited “a collection of strong resonances that were audible, but seemingly ignored or admired by many”.

The anechoic response for the AR-3 (1958) and AR-3a (1967 redesign) in the Toole text not only shows the downward sloped response, correlating the work of Roy Allison and Robert Berkovitz but also reveals diffraction problems from the lip on the front that holds the grille cloth along with issues from the simple cut-and-dry crossover.

The exploded view of the AR-3a

The history of Acoustic Research is all over the web and I will not repeat it here. Wikipedia is a good place to start. The mid-1970s saw a decline in sales under new ownership, and in 1993 the Boston facility was closed by yet another new owner and operations moved to California. There the AR-303 line was developed to be a modern loudspeaker that harkened back to the original ARs which did so well in the 50s and 60s.

The Californian team took advantage of the replacement parts for the 50s – 70s line still being produced in Japan. They updated the woofer and midrange drivers using parts with changes in materials, magnetics and adhesives advances that did not degrade with time. The tweeter was all-new with increased efficiency and power handling. The anechoic roll-off was gone. A new 3rd order crossover also prevented tweeter failure due to excessive levels.

The AR-303 speakers were vertically aligned as symmetrical matched pairs. The exploded view is shown in the figure below:

The exploded view of the AR-303

The grille was now a dust cover which, when removed, reveals the drivers on a flat baffle, moved to one side to significantly reduce diffraction.

The speakers were designed by AR alum Ken Kantor who was now at NHT along with his engineer Bill Bush. At NHT the state of the art 3.3 tower speaker appeared at about the same time. AR’s new owner had co-located the brand with NHT.

For those interested in all things AR the www.classicspeakerpages.net is the place to go and features a section on Ken Kantor discussing the design goals and the methods he used to realize those goals. That section can be found here.

I am not going to repeat this here for a speaker which went out of production in the late 1990s. Do not try to look up a pair of vintage AR-303 on eBay since the production was small. Most of what I saw online looked damaged or wildly overpriced.

The fact that the project to make new AR products, which were inspired by the originals, started in the early 90s, the founders of AR were still available to provide input as Ken Kantor explains:

“I read public and private engineering definitions of the original products, talked extensively to Vilchur, some to (Henry) Kloss, and other early employees and followers. Measured a great deal, then jumped in”.

My own quasi-anechoic nearfield measurements of the AR-302 are found on the Classic Speaker Page site.

The AR-302 is the redesign of the AR-5. The AR-302 is almost identical to AR-303 except for the smaller 10-inch woofer. The smaller woofer displays less directionality at the crossover to the midrange.

My measurement of the horizontal radiation pattern of the AR-302

I show only one measurement from the complete set at the above URL. I used a different display tool for this graph. This measurement looks like an excellent modern speaker and nothing like the anechoic measurements by Dr. Toole or what is found in the Allison and Berkovitz paper.

The transformation for this speaker came from the availability of the personal computer in the 90s and a whole series of CAD tools for the PC. These tools modeled the speakers, the resulting change in the speaker’s response when the drivers were placed in the box and synthesized a crossover to achieve the design targets. A quote from Ken Kantor on the Classic Speaker Site explains the process.

“We kept the essentials of the woofer and midrange. In other cases, like the crossover and tweeter, we decided that we could get closer to the intent of the 3a, et al, by taking a more modern route”.

“I don’t think about (crossover) circuit complexity, per se, unless there are tight cost constraints. In a design like the 303, all the attention goes to the acoustical response. I need half a dB less at 3 kHz, but move the main lobe down 15 degrees. A computer spits out a new circuit in a matter of seconds, and it is what it is”.
 
“In the old days, there was a lot of trial and error in designing a crossover. So, adding more than a few components was futile, since it wasn’t practically possible to optimize them. Simplicity yielded better optimizations”.
 
“The individual crossover components usually don’t have functions in a way that can be isolated. A crossover is a filter network that implements a transfer function as a result of all of its parts. Sometimes it is possible to generalize and say, Oh, this resistor adds damping. Or, This network compensates for a resonance. But, really, the better a crossover design is, the more the parts work together, symbiotically”.

My 9 point measurement of the in-room frequency response of the AR-302 in a 13 * 16 room

A slight slope downward with increasing frequency is noted, somewhat reminiscent of the new Harman Target curve but a little steeper. In my room, the AR-302 picked up some room modes to produce a response to 20Hz with the redesigned woofer and box. Ken Kantor and Bill Bush created a totally modern speaker in the 1990s.
 
My in-room response of the AR-302 looks reminiscent of an average of in-room responses of the AR-3A at 22 locations in 8 living rooms shown in figure 16 in the AES paper by Allison and Berkovitz cited above.

Comparing the AES paper results with my measurements above shows the roll-off above 2 kHz has a faster slope downward for the AR-3A measurement than my AR-302 measurement.

My 9 point measurement of the in-room frequency response of the AR-302 in a 13 * 16 room

The AES wants $33 for a PDF download of the Allison and Berkovitz paper. The price of academic papers is pushing up faster than prescription drugs. I wish you could see it to get an idea of the huge amount of work it took to create the figure above. Each of the 1/3 octave points in these curves (25 total) is hand calculated (remember this was 1972) from chart recorder plots at 22 locations. The chart recorder plots were in 1-decade spans, for accuracy, which carried over to the averaged plot above. I did my 9-point average in 10 minutes with at much higher resolution using DIRAC as the measurement Tool (REW would have worked just as well). In 47 years we have come a long way in making acoustic measurements.

Why the market at the time did not respond favorably to the AR-302 and AR-303 speakers is unclear. Perhaps it was the bookshelf design at first, which required very tall stands to achieve the best sound, but tower versions were sold a couple of years into production. These are likely the best of them and extremely rare.

The height was optimized for the optimal performance for the averaged seated listener. The increased box size extended the bass.

Again I am not trying to send you to eBay. New speakers are available that exceed the performance of the AR-303 series. What I am trying to show is the transformation that was made possible with modern CAD tools and driver production technology.

In 1991 Dr. Floyd Toole moved from the NRC in Canada to become a VP at Harman International. As part of his job as a corporate officer Dr. Toole built a new research group that subsequently produced a number of AES papers. JBL design engineers took the recommendations from this research group and in 1998 produced the JBL LSR32, JBL’s design teams also used a number of new materials and advanced CAD tools in the development of the LSR32.

The figure below is the exploded view.

The exploded view of the JBL LSR32

The 1998 LSR32 is not to be confused with the current JBL Synthesis L100 Classic and JBL Synthesis 4312G products. The JBL LSR32 used much higher quality parts and was designed to be used in a professional mix studio, not a home. Large bookshelf speakers, with an industrial look to keep costs down, continue to be a popular option in studios even today. The LSR32 form factor was dictated by what the professional mixing engineers wanted.

Later a cosmetic change resulted in a model number change called the LSR6332. This speaker continued to sell until a couple of years ago when JBL Pro ended the production of passive speakers (2017). It was good enough to be used as one of the references in the Harman listening labs.

The Harman spin curves for the LSR32 which was in production in early 1998.

The closest speaker to the LSR32, sold by Harman today for the home market, would be the Revel Performa F208. The tower F208 solves the optimum height of a bookshelf on stands issue, as the AR-302T did for that lineup in its day. The spin curve of the F208 is shown below.

The Harman spin curves for the Revel F208.

Today we no longer consider domestic loudspeakers to exhibit an East Coast or West Coast sound but, instead, a neutral sound when placed in an average listening room, free from driver resonance.

The start of this movement towards accurate loudspeaker sound reproduction in the 1990s should be considered a golden age of speaker evolution. New CAD tools, modern materials, and production techniques made the 90s the golden decade of speaker design. It was the designs by engineers at AR, NHT, Energy, PSB and Snell that ultimately brought it about. Progress has been made in the 2nd decade of the 21st century in passive speaker design but the best speakers of the early and mid-90s were closer than one would have expected. Now the future is in DSP based active speakers.

Acoustic Research Historian Tom Tyson supplied some comments on my article:

“AR’s philosophy was smooth and extended acoustic-power, and their reverberant-chamber response curves validated (to them) the importance of better off-axis response, even at the expense of on-axis smoothness, since it was felt that most listening would be well back in the listening room beyond the first-arrival sound.

Diffraction, lobbing and interference effects, of the AR-2 – AR-5, are less noticeable and less audible as one gets back into the reverberant sound field. If a microphone is placed at one meter in front of a speaker with these issues, and a chart recording is made and then compared to another recording with the mike placed in a different location, etc., it can be seen that there are nulls and voids which tend to cancel and are averaged-out in the reverberant field. I think that Toole and Olive and others tend to dictate quality objectives based on listening within a listening room with seating closer to the speakers for “localization,” and so forth. Note the location of the listening positions in the specialized room used by Toole. This would not be considered a “normal” listening position for many listeners, more of an audiophile-type setup that would favor more directional speakers (IMO) than those with a wide acoustic-power response”.